You might consider letting staff in for free. A lot of KOII, Michigan, and Minnesota comps let the staff in for free, and often times pay for their lunch. Your other route is to pay staff - but that's more difficult on your pocket, obviously. At my competition down here in Florida, not only did I feed my staff, but I also waived their fees, and took them all out to dinner once the competition is over.
If you want a helpful staff, you need to show them that it can be a two way street. Given the amount of competitions I've helped at - waiving fees is very standard. In fact, I generally opt to not help out at all unless that regulation comes into play. The idea is that if I'm a paying competitor, I shouldn't have to volunteer any more of my time than any other competitor.